Bricks are fired by either firewood or coal. Those fired by firewood take on black and blue color, and those by coal white. The temperature of coal-fired brick kiln is much higher than that fired by firewood.

T'ien-Kung K'ai-Wu (Exploiting the Works of Nature), by Sung Ying-hsing (1587-1663), a scientist in the late Ming and early Qing Dynasties, is an unprecedented comprehensive work on science and technology in ancient China.